This invention relates to a compact high pressure fluid operated cylinder and piston apparatus suitable for use, for example, for robotic grippers and the like, as illustrated in U.S. Pat. Nos. 4,566,727 and 4,492,400, together with a method of making and assembling same wherein the end caps are resiliently engaged between an O-ring adjacent an inner end and a snap ring adjacent an end of the cylinder to avoid leakage and chattering during operation.
The prior art contemplates utilizing a pair of spaced snap rings carried in grooves located on each side of an end cap for positioning same adjacent an end of a cylinder with an O-ring carried by a groove positioned wholly within the end cap intermediate the snap rings. Another prior art apparatus contemplates the use of a snap ring at the end of the cylinder on one side of the end cap while an inner portion of the end cap carries an O-ring and an intermediate shoulder is adapted to bear against a shoulder formed by a reduced bore within the cylinder. These devices require multiple steps in construction and do not lend themselves to compact construction in that the spaced snap rings, for example, require a cylinder of relatively substantial length. Moreover, the shoulder portions defined between the intermediate O-ring and the snap rings are reduced by the amount of the space occupied by the O-ring because the groove which accommodates the O-ring for sealing is of necessity relatively large since it is disposed entirely within the end cap and the shoulders are, therefore, more likely to fail in shear under high pressure within the cylinder.
Another disadvantage of the double snap ring construction resides in the fact that damage to the cylinder wall is likely to occur when inserting the inner snap ring and, because of the construction of the seal, leaking of the end cap is likely as a result of the positioning of the shoulders of the end cap between metallic snap rings opposite a damaged cylinder wall.
Accordingly, it is an important object of the invention to provide a structure for economical positioning of end caps within miniaturized cylinders wherein the end cap is positively positioned for reduced chattering with reduced length of cylinders.
Another important object of the invention is to provide an end cap structure for a cylinder and piston arrangement suitable for operation at a high pressure which may be economically constructed utilizing a snap ring on one side of the end cap on the outside thereof, while an O-ring is positioned within an intermediate groove or seat carried partially within the end cap and partially within an opposite portion of the cylinder wall.
Another important object of the invention is to provide a cylinder construction for use with high pressure apparatus which may be inexpensively constructed by lending itself to being severed in succeeded lengths from bar stock having an axial bore therein. The bar stock may be of any suitable length and may be round, square or otherwise multifaceted, depending upon the configuration desired for the cylinder.
Another important object of the invention is the provision of an end cap structure for a cylinder and piston arrangement suitable for operation without chattering of the end caps and without fluid leakage wherein the end cap is assembled so as to be resiliently squeezed or gripped between a resilient O-ring and a metallic snap ring.